JPH0347297B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene resin composition for foaming, and more specifically, to a composition capable of producing a polypropylene foam with excellent moldability, which can be foamed to a high magnification by heating. In general, polypropylene has strong mechanical strength and flexibility, as well as excellent heat resistance, chemical resistance, and electrical properties. Taking advantage of these characteristics, the development of foams using polypropylene is progressing. There is. The method that has been widely used up until now is
As shown in Japanese Patent No. 46-38716, there are many related to a method of crosslinking a specific propylene-ethylene copolymer and obtaining a foam sheet using decomposed gas of a known chemical blowing agent, and a method of producing polyethylene foam particles. There are methods introduced as a method for producing polyolefin foam particles, which is a superordinate concept of polypropylene, as if included in the disclosed technology. A common point in many of these documents is that in order to impart foaming ability to polypropylene, a crosslinking step of the base resin is always included. That is,
In the prior art, it was necessary to perform a resin crosslinking step prior to foaming. Recently, Japanese Patent Publication No. 56-1344 discloses a method for producing expanded particles made of non-crosslinked polypropylene resin. According to this technology, highly foamed particles can be obtained using a special method in which a foaming agent is contained in resin particles in an aqueous suspension system and then released all at once from a high temperature and high pressure region to a low pressure region. , special high-pressure equipment is required, and the temperature during foaming is just around the melting point of the base resin, so slight temperature differences or opening/closing conditions of the discharge pipe valve, in other words, pressure conditions during foaming, etc. Accordingly, the expansion ratio and bubble uniformity vary. Therefore, when producing a large amount of foamed particles industrially, the expansion ratio and the distribution of cell diameters are different for each batch, or even for the same batch at the initial stage and at the final stage, making it important to produce stably. However, there is still room for improvement before it can be put into practical use. Therefore, in the end, for foaming polypropylene resin, there is no choice but to use a widely known method of foaming resin particles containing a so-called foaming agent by heating them with a heating medium, but with this method, As for polypropylene, it is difficult to obtain highly foamed particles, and the current state is that highly foamed particles can only be obtained through multiple stages of foaming. In other words, according to this method, the efficiency of the blowing agent is low, and the heating process involves multiple stages, resulting in the consumption of a large amount of thermal energy, so that it cannot be adopted industrially. Furthermore, by repeating multiple cooling/heating cycles and stretching the bubble membrane, the melting point and crystallinity of the base resin itself rises, and the foamed particles are filled into a mold and heated to fuse the particles together. When a molded product is produced by using the same method, the resulting molded product has poor fusion properties between the particles, which has the disadvantage that it becomes impossible to obtain sufficiently satisfactory physical properties as a cushioning material. In view of these circumstances, the inventors of the present invention have carried out intensive research, and as a result have solved the above-mentioned drawbacks and completed an industrially applicable technology. An object of the present invention is to be able to produce a highly foamed material with virtually no crosslinking, and the foaming method can be as simple as conventionally used, and it has a uniform fine cell structure, has good cushioning properties, and has good resistance. It is an object of the present invention to provide a polypropylene resin composition for foaming, from which a highly foamed body having excellent chemical properties and heat resistance can be obtained. That is, the present invention uses polypropylene resins of 60 to 95
A polypropylene resin for foaming that can be foamed in a substantially non-crosslinked state by containing a blowing agent in a mixture of 5% to 40% by weight of aliphatic petroleum resin and/or alicyclic petroleum resin. It concerns a composition. The greatest feature of the present invention is that by mixing polypropylene resin and a specific petroleum resin,
The advantage is that a foam with a high magnification ratio can be obtained, and more specifically, a highly foamed article having uniform, fine cells can be obtained by simply heating the composition of the present invention with a heating medium. This fact is demonstrated in Table 2. In other words, according to the results in Table 2, heating only a composition containing a foaming agent in polypropylene resin (Experiment Nos. 10, 11, and 12) yields only foamed particles with low foaming; By mixing a cyclic petroleum resin and an aliphatic petroleum resin, it is possible to obtain a highly foamed body (Experiments Nos. 1 to 8). Moreover,
The uniformity of the bubbles in the foamed particles obtained is superior to that of the former. In general, petroleum resins include aliphatic petroleum resins, alicyclic petroleum resins, and aromatic petroleum resins.Among these, aromatic petroleum resins are made of highly foamed polypropylene as mentioned above. Almost no effect could be obtained (Experiment No. 13 in Table 2). Therefore, the petroleum resin applicable to the present invention is an aliphatic and/or alicyclic petroleum resin. The reason why such a petroleum-based resin greatly improves the foaming applicability of a polypropylene-based resin is not clear, but the present inventors think as follows. The mixture of the present invention has extremely high compatibility with each other, and also lowers the degree of crystallinity without lowering the crystalline melting point of polypropylene, and also lowers the softening temperature of the resin mixture. Therefore, the temperature difference between the softening point and the crystal melting point of the resin mixture increases, and even at temperatures above the softening temperature, polypropylene microcrystals exist and act as pseudo-crosslinking points, thereby widening the foaming temperature range. It is thought that this made it possible. In this respect, the technical concept is different from the conventional concept that a crosslinking reaction is essential for foaming polyolefin resins, and it has become possible to obtain highly foamed products with substantially no crosslinking.

【table】

[Table] Furthermore, by using the composition of the present invention, foamed particles with a high expansion ratio can be obtained without performing multistage foaming. As a conventional technique, in order to obtain a highly foamed product, there is a multi-stage foaming method in which a blowing agent is further injected into the primary foamed particles, and then heated and foamed repeatedly, but when this method is applied to foamed particles made of polypropylene resin alone, In order to reach a density of 0.030 g/cc as shown in the results of Experiment No. 15 in Table 3, three multistage foaming steps are required. In contrast, in the composition of the present invention, ie, Experiment No. 14 in Table 3, foamed particles with the same density of 0.031 g/cc can be obtained by only one foaming step. That is, by using the composition of the present invention, the amount of blowing agent used and the number of foaming steps can be reduced, resulting in a reduction in thermal energy. Furthermore, multiple foaming steps lead to a phenomenon in which the melting point of the polypropylene resin increases (see Table 3). Although the cause of this is not clear, it is thought that the heat treatment during foaming and the planar orientation of the foamed film interact to raise the melting point. Table 3 Experiment No.
15, when the melting point of foamed particles increases, it becomes necessary to heat the foamed particles to a temperature higher than the melting point when filling them into a mold that can be closed but cannot be sealed and molding them in the mold. This causes poor fusion between particles. However, the expanded particles obtained from the composition of the present invention do not require multistage foaming, and Table 3 Experiment No.
14, there is no increase in the melting point or the rate of increase is reduced. Furthermore, the softening point of the base resin is lower than that of polypropylene due to the mixture of petroleum-based resin, which enables good particle-to-particle fusion when forming expanded particles in a mold. The temperature range also expands to the lower temperature side, and the production of foamed molded products becomes stable and easy. In other words, when the molding temperature increases, the saturated vapor pressure of water vapor also increases, resulting in an increase in the pressure resistance of the equipment and an increase in the amount of steam used.However, this does not occur with the composition of the present invention, and it is economical. The ripple effects are significant.

【table】

[Table] Another feature of the composition of the present invention is that, as shown in Table 4, even when aliphatic or alicyclic petroleum resin is mixed, the buffering properties of the polypropylene foam alone are maintained. The heat resistance and chemical resistance are maintained with little deterioration. The conventional concept was that if other polymers were mixed with polypropylene resin in order to make it suitable for melt foaming, the resulting foam would have the disadvantage of losing its properties as a propylene resin. . However, it is surprising that this phenomenon does not occur in the composition of the present invention. The reason for this is thought to be that polypropylene has high compatibility with aliphatic and/or alicyclic petroleum resins and also has high rigidity.

[Table] Here, the mixing ratio of the aliphatic and/or alicyclic petroleum resin used in the present invention is based on the lower limit that enables high foaming of the polypropylene resin, the physical properties of the resulting foam, Among them, the heating dimensional change that is most susceptible is selected within a range that causes no practical problems.
Experiment No. 1 to 4, 10 in Table 1 and Experiment No. 16 to Table 4
Referring to Figure 1 of this section, which was obtained from the results of No. 20, the mixing ratio is 95 to 60% polypropylene resin.
% by weight and aliphatic petroleum resin and/or alicyclic petroleum resin from 5 to 40% by weight. Furthermore, considering the ease of kneading the resins together, it is preferable that the amount of the above-mentioned petroleum resin be 10 to 30% by weight. The polypropylene resin used in the present invention includes various types of copolymers such as propylene homopolymer, block, random, and graft polymers containing 50% by weight or more of propylene and one or more other copolymerizable monomers. It is a polymer or a blend mainly composed of any of these. For example, ethylene-propylene block copolymer, ethylene-propylene-random copolymer, ethylene-propylene-butene-1-random copolymer, propylene homopolymer or the above copolymer and low density polyethylene, Examples include mixtures with high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer rubber, styrene-butadiene copolymer rubber, and the like. Among these, ethylene-
Propylene-butene-1-random copolymer is good. These petroleum resins, which are essential constituents to be mixed with polypropylene polymers, are obtained by polymerizing C ₄ to _{C 9} fractions produced during cracking of petroleum, naphtha, and the like. Aliphatic petroleum resins are C ₄ and C ₅ fraction olefins,
Diolefins are obtained by polymerizing with a Friedel-Crafts catalyst using, for example, isobutylene, butadiene, isobrene, piperine, etc. as main components, and have an average molecular weight of 300 to 10,000. Specific examples of aliphatic petroleum resins include Hiretsu from Mitsui Petrochemicals, Escorets from Tonen Petrochemicals, Quinton from Nippon Zeon, and Tatsukiroll from Sumitomo Chemical. Alicyclic petroleum resins are obtained by polymerizing alicyclic fractions such as cyclopentadiene and dicyclopentadiene, or by hydrogenating aromatic petroleum resins. Here, aromatic petroleum resins are C ₉ and C ₁₀ fractions,
For example, it is a resin whose main component is vinyltoluene, indene, methylindene, etc. as a polymerization raw material. By hydrogenating this resin, it becomes a colorless and transparent resin, and becomes an alicyclic petroleum resin. Specific examples of this resin include Arakawa Chemical Co., Ltd.'s Alcon,
There are Quinton 1500, 1700, etc. made by Zeon Corporation. The softening point of petroleum resin in steam is ASTM E-28-
67 ball & ring method at 80-100℃, preferably
A temperature range of 90 to 150°C is used. The softening point of the petroleum resin is appropriately selected based on the degree of heating dimensional stability required for the target polypropylene resin foam and the kneadability of the polypropylene polymer, that is, the range that allows uniform kneading. The temperature difference between the softening point and the crystal melting point can be set according to the purpose. Any known method can be used to incorporate the blowing agent into the resin mixture, and the method can be selected depending on the purpose. For example, a polypropylene resin and a petroleum resin are kneaded in advance using an extruder, a Banbury mixer, a kneader roller, etc. to form mixed resin particles, and then the particles are placed in a closed container and a volatile organic blowing agent is introduced. In the case of chemical blowing agents, there are two methods: directly impregnating under heat and pressure or in an aqueous suspension system, or when mixing two types of resins, adding or press-injecting a blowing agent at the same time under heat and melting. The above-mentioned mixing device can be used as is, and if the foaming agent is a volatile foaming agent, a method of press-fitting the foaming agent into the heated and melted state of the resin in the extruder can be used. The blowing agents used in this case are ordinary chemical blowing agents and volatile blowing agents. Particularly preferred are volatile organic blowing agents, and any blowing agent that boils below the melting point of the resin mixture may be used. Typical examples include aliphatic hydrocarbons such as propane, butane, pentane, and hexane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, and trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, and methyl chloride. , ethyl chloride, methylene chloride, and other halogenated hydrocarbons. Chemical blowing agents include azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, paratoluenesulfonylhydrazide, and the like. In order to obtain a foam from the foaming composition of the present invention, a known method can be used in which foaming is carried out in a temperature range of above the softening point of the resin mixture and below the crystal melting point +10°C.
For example, particles of the resin mixture described above are impregnated with a blowing agent directly or in an aqueous suspension in a closed container, cooled, taken out and air-dried, and then heated with a heating medium such as steam to a temperature above the softening point of the resin mixture. A method of heating and foaming the resin mixture to a temperature below the crystal melting point + 10℃, in which particles of the resin mixture are impregnated with a foaming agent in a water suspension system in a closed container under high temperature and pressure.
There are methods for foaming by blowing it all at once into a low-temperature, low-pressure region in a temperature range of 10°C or less, and methods for adding or press-feeding a foaming agent to a resin mixture while heating and melting it, and then extruding it into a low-pressure region. You can select both. The composition of the present invention is effective over the above-mentioned method, which involves a step of impregnating a premixed resin mixture with a blowing agent. This method is effective for foaming methods. In order to give the expanded polypropylene resin particles produced as described above the ability to expand within a mold, a process of increasing the internal pressure of the particles or compressing the particles, filling the particles into a mold, and foaming the particles is performed. A foamed molded product is finally obtained through the steps of foaming and heat-sealing the particles to form a foam molded product according to the shape, cooling and taking out the foamed molded product, and further aging the foamed molded product. It will be done. The softening point of the foamed particles obtained from the composition of the present invention decreases depending on the softening point and mixing ratio of the petroleum resin. is improved compared to the case of polypropylene resin alone, and has the advantage of being able to be heated at a low temperature and widening the heating temperature range during molding. As described above, the polypropylene resin foam obtained from the composition of the present invention makes full use of the properties of polypropylene resin, has excellent heat resistance, chemical resistance, flexibility, etc., and has sufficient rigidity. It is something. The evaluation method and evaluation criteria for the characteristics evaluated in the present invention will be described below. Uniformity of bubbles Approximately 20 foamed particle samples were visually observed in a cross section cut at the center section under 50x magnification.

[Table] Melting point measurement Using DSC (manufactured by Perkin-Elmer),
10 mg was weighed out and measured according to a conventional method at a heating rate of 10°C/min, and the top of the melting peak was taken as the melting point. Characteristics of molded products (1) Degree of fusion 100 x 100 mm from parts of molded products with a thickness of 20 mm or more
Cut out a square test piece and make a 2-deep hole in the center.
A cut of mm was made, and the molded product was bent and split along the cut, and the percentage of the number of particles that were broken and torn relative to the total number of particles present in the cut cross section was determined. Evaluation criteria

[Table] (2) Density Measured according to JIS K6767. (3) Compression set Measured according to JIS K6767. The test conditions were 25% constant compression. (4) Measured according to JIS K6767. The test conditions were 25% constant compression. (5) Heating dimensional change A molded sample cut into a 200 mm square was heated at 25°C.
Let it stand for 24 hours, then draw a square of 100 x 100 mm and a central cross in the center and measure the length of each line segment accurately.
In a constant temperature bath controlled at 100℃±1℃

[Table] After being left to stand still for 96 hours, the sample was taken out and left to cool at 25°C for 1 hour. The dimensions of the marked lines were precisely measured, and the rate of change (%) from the original dimensions was determined, and the average value was determined. Evaluation Criteria: Less than 4%: No practical problem More than 4%: Not usable Below, the present invention will be explained in detail with reference to Examples.
The resins used in the examples are those shown in Table 1. Examples, Comparative Example 1 Polypropylene shown in Table 1 and petroleum resin were dry blended at the mixing ratio shown in Table 2, and a 40mmφ
The mixture was melt-kneaded using a single-screw extruder to create pellets with a diameter of approximately 2.5 mm. For 100 parts by weight of the mixed resin particles, 400 parts by weight of water, 1 part by weight of polyvinyl alcohol (Gohsenol GH-17, Nippon Gosei Co., Ltd.) and 30 parts by weight of dichlorodifluoromethane were placed in a closed container, and the mixture was heated to 80 parts by weight while stirring. The temperature was raised to .degree. C., maintained for 0.5 hours, cooled, and the resin particles impregnated with the foaming agent were taken out, air-dried, and immediately heated with steam to obtain primary foam particles. The foaming temperature at this time, the density and melting point of the foamed particles,
Table 2 shows the results of evaluating the uniformity of bubbles according to the method described in the text. From the results of Experiment Nos. 1 to 4 and 10 in Table 2, it is clear that compared to foaming polypropylene alone, by mixing petroleum resin, high foaming can be achieved with only primary foaming, and that the foaming temperature It is clear that this can be reduced. Furthermore, the uniformity of the bubbles in the expanded particles is also improved. Furthermore, comparing Experiment Nos. 7 and 8 with 11 and 12, even with polypropylene, propylene homopolymer and ethylene-propylene block copolymer tend to have higher foaming temperatures and lower expansion ratios, but the present invention It is clear that this drawback is improved by creating a composition of 1, and that a propylene copolymer having a specific composition is not necessarily required. Example, Comparative Example 2 Experiment on the density of primary foam particles in Experiment No. 10 in Table 2
In order to equalize the density of No. 3 primary foamed particles, the internal pressure of the foamed particles should be approximately 1.6Kg/cm ² (gauge pressure).
Air was injected into the container under pressure at 80° C. and 10 kg/cm ² so that the resultant mixture was heated and foamed immediately with water vapor. By repeating this process and performing tertiary foaming, expanded particles with a density of 0.030 g/cc were finally obtained. Regarding the foamed particles No. 10′ obtained in this way,
Table 3 shows the foaming temperature, the efficiency of the foaming agent, the density of the foamed particles, and the melting point of the resin constituting the foamed particles in comparison with the foamed particles of Experiment No. 3. Furthermore, the internal pressure was 1.0 for the primary foamed particles of Experiment No. 3 and the particles of Experiment No. 10 (tertiary foamed) described above.
Immediately inject air at 80℃ ^{and 10Kg/cm 2 to} obtain a particle size of 120 x 120 x 30 mm ³
The mixture was filled into a mold for forming a plate-like product, and heated with steam to form a molded product. In this case, 1 kg/cm ² of water vapor is used for heating.
With 15 seconds of preheating and the steam pressure shown in Table 3.
The mold was heated for 10 seconds, then cooled and taken out. The molded body taken out was aged in a room at 90°C for 8 hours. Table 3 shows the density of each molded body obtained and the degree of fusion based on the evaluation method described in the text. From the above results, it can be seen that the density of foamed particles reached by three times of high-order foaming in the composition of only polypropylene is the same as that achieved in one foaming process with the composition of the present invention. This makes it possible to reduce the number of processes, reduce utility costs, and have a large economic ripple effect. Furthermore, as the number of foaming increases, a phenomenon is observed in which the melting point of the constituent resin increases. The cause of this is not clear, but since heating above the melting point of the constituent resin is required to fuse the particles together during in-mold molding, this increase in the melting point may impede the fusion properties between the particles. , and further increases the amount of steam consumed, resulting in a disadvantage. moreover,
As the pressure of the heated steam increases, the pressure resistance of the molding machine itself must be increased. However, the expanded particles made of the composition of the present invention have a small number of foaming times and a small increase in melting point, and therefore are found to be extremely advantageous from an industrial perspective. Example 3 The primary expanded particles of Experiment Nos. 1 and 2 in Table 2 were subjected to secondary foaming in the same manner as in Example 2, and the primary expanded particles of Experiment No. 6 were used as Example 2. An in-mold molded body was obtained by the same method. Table 4 shows the results of measuring the physical properties of the molded bodies thus obtained and the molded bodies obtained in Examples and Comparative Example 2 according to the evaluation method described in the text. From the results in Table 4, it is clear that the molded article made of the composition of the present invention has a higher degree of fusion than the molded article made only of polypropylene, and requires less steam pressure for molding. It can also be seen that the physical properties of the molded product, such as compressive strength and compression set, are comparable to those of a molded product made only of polypropylene. Here, the density and petroleum resin content of the primary foam particles of Experiment Nos. 1, 2, 3, 4, and 10 in Table 2, and the foam molding of Experiments No. 16, 17, 18, 19, and 20 in Table 4 Figure 1 shows the relationship between the dimensional change of the body upon heating and the petroleum resin content.
From this drawing, it is clear that a petroleum resin content in the range of 95 to 60% allows for high foaming and maintains the properties as a polypropylene foam. As explained above, the present invention is considered to have high industrial utility value.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the change in the density of the primary foamed particles and the dimensional change (%) on heating of the foamed molded product as the petroleum resin content (% by weight) changes in the composition of the present invention.

Claims (1)

[Claims] 1 60 to 95% by weight of polypropylene resin and 5 to 95% by weight of aliphatic petroleum resin and/or alicyclic petroleum resin
A foaming polypropylene resin composition that contains a foaming agent in a mixture of 40% by weight and can be foamed in a substantially non-crosslinked state.